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Conference paperLin ZL, Chen W, Zhang G, et al., 2025,
Sub-50-fs in-Band Pumped Tm, Ho-Codoped 'Mixed' Calcium Aluminate Laser
We report on a mode-locked Tm, Ho:Ca(Gd,Y)AlO<inf>4</inf> laser in-band pumped by a Raman fiber laser at 1678 nm, generating 48-fs pulses slightly above 2μ m with an average power of 109 mW at 72.5 MHz.
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Journal articleTaylor JR, 2025,
Wilson Sibbett (1948-2024) Obituary
, NATURE PHOTONICS, Vol: 19, Pages: 1-2, ISSN: 1749-4885 -
Conference paperKrawczyk B, Kudlinski A, Battle RA, et al., 2025,
Enhanced four-wave mixing in the normal dispersion regime of a Yb-doped photonic crystal fiber
, 2025 Conference on Nonlinear Frequency Generation and Conversion, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X -
Journal articleKoufidis SF, Koutserimpas TT, Monticone F, et al., 2024,
Electromagnetic wave propagation in time-periodic chiral media
, OPTICAL MATERIALS EXPRESS, Vol: 14, Pages: 3006-3029, ISSN: 2159-3930 -
Journal articleTan Q, Riemer K, Hansen-Shearer J, et al., 2024,
Transcutaneous imaging of rabbit kidney using 3-D acoustic wave sparsely activated localization microscopy with a row-column-addressed array
, IEEE Transactions on Biomedical Engineering, Vol: 71, Pages: 3446-3456, ISSN: 0018-9294Objective: Super-resolution ultrasound (SRUS) imaging through localizing and tracking microbubbles, also known as ultrasound localization microscopy (ULM), can produce sub-diffraction resolution images of micro-vessels. We have recently demonstrated 3-D selective SRUS with a matrix array and phase change contrast agents (PCCAs). However, this method is limited to a small field of view (FOV) and by the complex hardware required. Method: This study proposed 3-D acoustic wave sparsely activated localization microscopy (AWSALM) using PCCAs and a 128+128 row-column-addressed (RCA) array, which offers ultrafast acquisition with over 6 times larger FOV and 4 times reduction in hardware complexity than a 1024-element matrix array. We first validated this method on an in-vitro microflow phantom and subsequently demonstrated non-invasively on a rabbit kidney in-vivo. Results: Our results show that 3-D AWSALM images of the phantom covering a 25×25×40 mm 3 volume can be generated under 5 seconds with an 8 times resolution improvement over the system point spread function. The full volume of the rabbit kidney can be covered to generate 3-D microvascular structure, flow speed and direction super-resolution maps under 15 seconds, combining the large FOV of RCA with the high resolution of SRUS. Additionally, 3-D AWSALM is selective and can visualize the microvasculature within the activation volume and downstream vessels in isolation. Sub-sets of the kidney microvasculature can be imaged through selective activation of PCCAs. Conclusion: Our study demonstrates large FOV 3-D AWSALM using an RCA probe. Significance: 3-D AWSALM offers an unique in-vivo imaging tool for fast, selective and large FOV vascular flow mapping.
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Journal articleKoufidis SF, Lakhtakia A, Mccall MW, 2024,
Comment on 'No circular birefringence exists in a chiral medium: an analysis of single-mode refraction'
, NEW JOURNAL OF PHYSICS, Vol: 26, ISSN: 1367-2630 -
Journal articleXiao H, Damzen MJ, 2024,
High-efficiency 5-watt wavelength-tunable UV output from an Alexandrite laser
, APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 130, ISSN: 0946-2171 -
Journal articleBharadwaj A, Kumar A, Kalita R, et al., 2024,
Super-resolved fluorescence imaging utilising accessible stochastic optical reconstruction microscopy (easySTORM) implemented on a low-cost, modular open-source (openFrame) microscope
, Measurement Science and Technology, Vol: 35, ISSN: 0957-0233Optical super-resolution microscope is a powerful tool for the life sciences, including cell biology and pathology yielding information on, e.g. biological structure and protein distribution in the nano-scale range. In recent years, there has been an exponential rise in the interest to apply super-resolution microscopes in diverse areas, but its wider utility is hindered by the cost of purchasing and maintaining super-resolved microscopes. In this paper we present the implementation of easySTORM, an accessible implementation of stochastic optical reconstruction microscopy (STORM) at Indian Institute of Technology Guwahati (IITG), India, in a flexible, user friendly and cost-effective manner using a state-of-the-art, modular, open-source, optical microscope platform called: 'openFrame'. Providing comparable imaging performance to commercial optical super-resolution microscopes, the openFrame-based implementation of easySTORM uses in-expensive multimode diode lasers and industry grade CMOS cameras, and the open-source and modular nature of the instrument makes it easy to maintain and to upgrade. To demonstrate its successful implementation at IITG, we image quantum dots and actin-tubulin structure in both normal and cancer cells, resolved features separated by a few tens of nanometers. This work demonstrates that openFrame-enabled easySTORM instrumentation can be widely accessible to provide affordable, research grade super-resolution microscopy capability for academic and medical research.
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Journal articleDe Corte A, Koufidis SF, Mccall MW, et al., 2024,
Exceptional points in negatively refracting chirowaveguides due to giant chirality
, PHYSICAL REVIEW A, Vol: 110, ISSN: 2469-9926 -
Conference paperJiang X, Xiao H, Damzen MJ, 2024,
Transient Analysis of Pump-induced Lensing Effects in Alexandrite Lasers Using Pump-Probe Technique
, ISSN: 2101-6275A novel transient pump-probe method is used to differentiate thermal and population pump-induced lensing mechanisms. In diode-pumped Alexandrite lasers, excellent agreement is found between theory and experiment and the population lens is found to be dominant in non-lasing amplifier.
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Conference paperXiao H, Damzen MJ, 2024,
5-Watt level widely wavelength-tunable UV output from a frequency-doubled Alexandrite laser
, ISSN: 2101-6275We demonstrate a record 5-Watt level, wavelength tunable, continuous-wave UV output based on a diode-pumped Alexandrite laser employing intra-cavity second harmonic generation. A wide wavelength tuning range from 364nm to 402nm was achieved.
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Conference paperDamzen MJ, 2024,
Alexandrite Lasers: Review of recent laser progress and developments for vegetation lidar
, ISSN: 2101-6275A review is made of recent progress in diode-pumped Alexandrite lasers as a high-power, tunable-wavelength source, and our advances in developing Alexandrite as a short-pulse, high-pulse-rate vegetation lidar source for satellite-based Earth Observation.
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Journal articleBoland MA, Lightley JPE, Garcia E, et al., 2024,
Model-free machine learning-based 3D single molecule localisation microscopy
, Journal of Microscopy, ISSN: 0022-2720<jats:title>Abstract</jats:title><jats:p>Single molecule localisation microscopy (SMLM) can provide two-dimensional super-resolved image data from conventional fluorescence microscopes, while three dimensional (3D) SMLM usually involves a modification of the microscope, e.g. to engineer a predictable axial variation in the point spread function. Here we demonstrate a 3D SMLM approach (we call<jats:italic>“easyZloc”</jats:italic>) utilising a lightweight Convolutional Neural Network that is generally applicable, including with “standard” (unmodified) fluorescence microscopes, and which we consider may be practically useful in a high throughput SMLM workflow. We demonstrate the reconstruction of nuclear pore complexes with comparable performance to previously reported methods but with a significant reduction in computational power and execution time. 3D reconstructions of the nuclear envelope and a tubulin sample over a larger axial range are also shown.</jats:p>
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Journal articleKoufidis SF, Koutserimpas TT, Monticone F, et al., 2024,
Enhanced scattering from an almost-periodic optical temporal slab
, PHYSICAL REVIEW A, Vol: 110, ISSN: 2469-9926 -
Journal articleLerendegui M, Riemer K, Papageorgiou G, et al., 2024,
ULTRA-SR challenge: assessment of UltrasoundLocalization and TRacking algorithms for super-resolution imaging
, IEEE Transactions on Medical Imaging, Vol: 43, Pages: 2970-2987, ISSN: 0278-0062With the widespread interest and uptake of super-resolution ultrasound (SRUS) through localization and tracking of microbubbles, also known as ultrasound localization microscopy (ULM), many localization and tracking algorithms have been developed. ULM can image many centimeters into tissue in-vivo and track microvascular flow non-invasively with sub-diffraction resolution. In a significant community effort, we organized a challenge, Ultrasound Localization and TRacking Algorithms for Super-Resolution (ULTRA-SR). The aims of this paper are threefold: to describe the challenge organization, data generation, and winning algorithms; to present the metrics and methods for evaluating challenge entrants; and to report results and findings of the evaluation. Realistic ultrasound datasets containing microvascular flow for different clinical ultrasound frequencies were simulated, using vascular flow physics, acoustic field simulation and nonlinear bubble dynamics simulation. Based on these datasets, 38 submissions from 24 research groups were evaluated against ground truth using an evaluation framework with six metrics, three for localization and three for tracking. In-vivo mouse brain and human lymph node data were also provided, and performance assessed by an expert panel. Winning algorithms are described and discussed. The publicly available data with ground truth and the defined metrics for both localization and tracking present a valuable resource for researchers to benchmark algorithms and software, identify optimized methods/software for their data, and provide insight into the current limits of the field. In conclusion, Ultra-SR challenge has provided benchmarking data and tools as well as direct comparison and insights for a number of the state-of-the art localization and tracking algorithms.
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Journal articleHansen-Shearer J, Yan J, Lerendegui M, et al., 2024,
Ultrafast 3-D Transcutaneous Super Resolution Ultrasound Using Row-Column Array Specific Coherence-Based Beamforming and Rolling Acoustic Sub-aperture Processing: In Vitro, in Rabbit and in Human Study
, ULTRASOUND IN MEDICINE AND BIOLOGY, Vol: 50, Pages: 1045-1057, ISSN: 0301-5629 -
Journal articleDarling C, Kumar S, Alexandrov Y, et al., 2024,
Optical projection tomography implemented for accessibility and low cost (OPTImAL)
, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 382, ISSN: 1364-503XOptical projection tomography (OPT) is a three-dimensional mesoscopic imaging modality that can use absorption or fluorescence contrast, and is widely applied to fixed and live samples in the mm-cm scale. For fluorescence OPT, we present OPT implemented for accessibility and low cost, an open-source research-grade implementation of modular OPT hardware and software that has been designed to be widely accessible by using low-cost components, including light-emitting diode (LED) excitation and cooled complementary metal-oxide-semiconductor (CMOS) cameras. Both the hardware and software are modular and flexible in their implementation, enabling rapid switching between sample size scales and supporting compressive sensing to reconstruct images from undersampled sparse OPT data, e.g. to facilitate rapid imaging with low photobleaching/phototoxicity. We also explore a simple implementation of focal scanning OPT to achieve higher resolution, which entails the use of a fan-beam geometry reconstruction method to account for variation in magnification. This article is part of the Theo Murphy meeting issue 'Open, reproducible hardware for microscopy'.
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Journal articleLerendegui M, Yan J, Stride E, et al., 2024,
Understanding the effects of microbubble concentration on localization accuracy in super-resolution ultrasound imaging
, PHYSICS IN MEDICINE AND BIOLOGY, Vol: 69, ISSN: 0031-9155 -
Journal articleDent LG, Curry N, Sparks H, et al., 2024,
Environmentally dependent and independent control of 3D cell shape
, CELL REPORTS, Vol: 43, ISSN: 2211-1247 -
Journal articleRiemer K, Tan Q, Morse S, et al., 2024,
3D Acoustic Wave Sparsely Activated Localization Microscopy With Phase Change Contrast Agents
, INVESTIGATIVE RADIOLOGY, Vol: 59, Pages: 379-390, ISSN: 0020-9996 -
Journal articleZeng H-J, Xue W-Z, Murray RT, et al., 2024,
In-band pumped Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser
, Optics Express, Vol: 32, Pages: 16083-16089, ISSN: 1094-4087We report on a Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser with in-band pumping of the Tm ions by a spatially single-mode 1678 nm Raman fiber laser. The structurally disordered CaGdAlO4 host crystal is also codoped also with the passive Lu ion for additional inhomogeneous line broadening. The Tm,Ho,Lu:CaGdAlO4 laser generates soliton pulses as short as 79 fs at a central wavelength of 2073.6 nm via soft-aperture Kerr-lens mode-locking. The corresponding average output power amounts to 91 mW at a pulse repetition rate of ∼86 MHz. The average output power can be scaled to 842 mW at the expense of slightly longer pulses of 155 fs at 2045.9 nm, which corresponds to a peak power of ∼58 kW. To the best of our knowledge, this represents the first demonstration of an in-band pumped Kerr-lens mode-locked Tm,Ho solid-state laser at ∼2 µm.
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Journal articleTemel T, Murray RT, Wang L, et al., 2024,
Narrowband-seeded PPLN non-resonant optical parametric oscillator
, Optical Materials Express, Vol: 14, Pages: 889-895, ISSN: 2159-3930A PPLN non-resonant optical parametric oscillator injection-seeded by narrowband sub-100-mW CW radiation at the signal wavelength produces > 3 W idler average power at 2376 nm for a 20-kHz repetition rate, with a sub-2-nm spectral linewidth. The maximum quantum efficiency reaches 39.5%, roughly 1.4 times higher compared to narrowband operation achieved with a volume Bragg grating at the same pump level. Seed levels as low as 40 mW are sufficient to produce the desired spectral narrowing effect.
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Journal articleXiao H, Jiang X, Damzen MJ, 2024,
Transient pump-probe analysis of pump-induced lensing in laser amplifiers
, Optics Express, Vol: 32, Pages: 12783-12799, ISSN: 1094-4087Understanding of pump-induced lensing in laser amplifiers is essential for the optimized design of high-power lasers with high spatial quality, but there is usually incomplete knowledge of the interplay between thermal and population induced lensing mechanisms, lensing under lasing and non-lasing conditions, and transient lensing effects under pulsed operation. This paper provides quantitative insight of pump-induced lensing effects by using experimental transient pump-probe measurements in an alexandrite laser amplifier end-pumped by a short pulse pump beam with Gaussian spatial intensity distribution. Lensing results are presented showing a large difference in lensing under both non-lasing and lasing conditions and distinction of the population lens and thermal lens contributions from their different response time. Different pump beam sizes are used to show the variation of the relative strength of the lensing mechanisms. Comparison of experimental results with the analytical transient theory developed in this paper for the Gaussian pump beam gives excellent agreement and quantitative information on the thermal and population contributions to the amplifier lens. This paper provides a methodology for quantitative investigation of pump-induced lensing in general laser amplifier systems, and potentially other classes of optical materials with residual optical absorption.
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Conference paperCodescu M-A, Murray JM, Zawilski KT, et al., 2024,
Optical Parametric Generation in Non-Critically Cut CdSiP2 with a Nanosecond 1.064 μm Nd:YAG Laser
, Optica High-Brightness Sources and Light-Driven Interactions Congress -
Conference paperMurray RT, Battle RA, Simon D, et al., 2024,
Visualizing metabolites at the cellular level: advancements in 3-micron laser desorption mass spectrometry imaging
, SPIE BiOS, Publisher: SPIE, Pages: 4-4By combining high beam quality picosecond pulsed optical parametric amplifiers at 2.94 μm with Rapid Evap-ortive Ionisation Mass Spectrometry (REIMS), we have demonstrated record spatial pixel resolutions for ambientmass spectrometry (MS) imaging of < 10 μm. In this contribution, we introduce our work in this area, demon-strating the platform workflow and highlighting recent results of metabolic imaging at the single cell resolutionlevel.
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Journal articleTemel T, Murray RT, Wang L, et al., 2024,
Energy scaling of a narrowband, periodically poled LiNbO₃, nanosecond, nonresonant optical parametric oscillator
, Applied Optics, Vol: 63, Pages: 1811-1814, ISSN: 1559-128XWe demonstrate that 3-mm-thick, periodically poled LiNbO₃ enables energy scaling of a nonresonant optical parametric oscillator operated in the narrowband mode with a volume Bragg grating at the signal wavelength. Utilizing the full available pump power at 1064 nm, we obtained maximum average powers of 2.25 and 2.08 W for the signal (1.922 µm) and idler (2.383 µm) pulses at 10 kHz, at a total conversion efficiency of 32.8%, which represents a fourfold increase in terms of peak powers over our previous work. The signal and idler spectral linewidths were ∼ 1 nm, with pulse lengths of ∼ 6 ns and an idler beam propagation factor of ∼5.
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Journal articleBharadwaj A, Kalita R, Kumar A, et al., 2024,
A cost-effective, modular, research-grade optical microscope
, CURRENT SCIENCE, Vol: 126, Pages: 244-254, ISSN: 0011-3891 -
Conference paperMurray JM, Codescu M-A, Zawilski KT, et al., 2024,
Optical Parametric Generation in Non-Critically Cut CdSiP2 with a Nanosecond 1.064 μm Nd:YAG Laser
, Optica High-Brightness Sources and Light-Driven Interactions Congress -
Conference paperDas S, Temel T, Murray RT, et al., 2024,
Power Scaling of a Narrowband PPLN Non-Resonant Optical Parametric Oscillator
Using a Volume-Bragg-Grating at the signal wavelength in a periodically-poled LiNbO<inf>3</inf> (PPLN) non-resonant optical parametric oscillator we achieve a total average power of 11.35 W at 20 kHz corresponding to a conversion efficiency of 63%.
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Conference paperChen W, Lin ZL, Griebner U, et al., 2024,
Phase- and group-locked vector solitons in a femtosecond mode-locked Ho-laser
Group-velocity locked vector solitons are observed in a mode-locked femtosecond solid-state laser at ~2 μm. Under certain conditions, stable phase-locking of the two polarizations occurs in the soliton regime: a phase- and group-locked vector soliton.
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